A process of the type mentioned in the introduction for manufacturing catalytic converters, especially for manufacturing motor vehicle catalytic converters, is generally known. A catalytic converter housing, which may have a great variety of cross-sectional shapes corresponding to the particular intended use, e.g., a round, oval or elliptical shape, is first manufactured according to the prior-art process by forming and welding. At least one monolith, which is manufactured from a porous ceramic material, is coated with catalyst material, and whose cross section is adapted to the cross-sectional shape of the catalytic converter housing, is stuffed into the catalytic converter housing during the subsequent operation, the so-called canning. Depending on the particular application, two or more monoliths may also be stuffed into the catalytic converter housing, and, if necessary, they are arranged at spaced locations from one another in the catalytic converter housing. The catalytic converter housing is closed after the canning, e.g., by fastening corresponding connection flanges and covers.
Due to the ceramic material used, the monolith is relatively susceptible to shocks. Any movement of the monolith in relation to the catalytic converter housing must therefore be prevented from occurring to the extent possible in order to prevent the monolith from being damaged. The monolith should also not be set to vibrate due to vibrations of the catalytic converter housing, which are transmitted, e.g., from the motor vehicle to the catalytic converter housing, or by pulsating exhaust gas flows which flow through the monolith.
To guarantee this, a mounting mat made of glass fibers, rock wool or a similar heat resistant and shock-absorbing material is usually fastened around the outer circumferential surface of the monolith, i.e., the surface that extends rotationally symmetrically to the body axis of the monolith, along which the monolith is stuffed into the catalytic converter housing. The mounting mat assumes essentially two functions. On the one hand, the mounting mat shall keep the monolith under pretension in the catalytic converter housing in order to prevent a relative movement between the monolith and the catalytic converter housing. On the other hand, the mounting mat shall effectively absorb vibrations acting on the catalytic converter housing in relation to the monolith.
To fasten the mounting mat to the monolith, the monolith is usually wrapped up manually in the mounting mat and fixed by means of an adhesive to the monolith. However, the drawback of this procedure is that the quality of the positioning of the mounting mat at the monolith is greatly affected by the individual skill and the individual performance capacity of the worker who fastens the mounting mat to the monolith.
Thus, folds, which make it difficult or even impossible to stuff the monolith provided with the mounting mat into the catalytic converter housing, may be formed during the wrapping up of the monolith in the mounting mat, or a gap may be left at the two mutually abutting lateral edges of the mounting mat during the assembly of the mounting mat, and this gap will form a bypass with the monolith stuffed into the catalytic converter housing, along which exhaust gas can flow untreated through the catalytic converter housing in parallel to the monolith. Furthermore, permanent fastening of the mounting mat with a hot-melt adhesive is not always guaranteed, so that the mounting mat may separate, especially during the canning, and the manufacturing process is interrupted. Since experience has shown that the time necessary for the assembly varies greatly in such an assembly step—it depends on the skill of the particular worker—integration of the winding in an automatic manufacturing cycle is possible with a corresponding intermediate buffer only. Despite the intermediate buffer, canning may be interrupted in case of an excessively long assembly time by the preceding wrapping up of the monolith in the mounting mat, which is performed manually, i.e., the canning machines are briefly out of use. Due to the large lot sizes in which catalytic converters are usually manufactured, this leads to high additional costs.
Segmented folding tools, which are to automatically wrap up the monolith in the mounting mat, have therefore also been used for some time. The folding tool has for this purpose a plurality of arc-shaped folding segments, which are articulated to one another and are activated one after another and lay the mounting mat section by section around the monolith. The drawback of such folding tools is, on the one hand, that the individual folding segments of the folding tool are to be actuated individually, which requires a considerable effort for control, and the folding tool consequently has to be complicated. On the other hand, the mounting mat is often creased at the transition between two folding segments, which may lead to damage to the structure of the mounting mat, which may lead as a consequence to the formation of the above-mentioned bypasses.